It was used to target tunnels

The target was ISIS tunnels and caves deep in a remote, mountainous area of Afghanistan.

"In this area, mountains and caves, you want something that can get a blast effect into the caves and tunnels," CNN military analyst Rick Francona said on "Inside Politics" on Thursday.

"And this is the weapon to do that, the overpressure from the weapon will send shock waves through the tunnel systems and that will kill almost everybody in there within a certain range."

That is why you use this weapon ... it will set off a huge blast, it will feel like a nuclear weapon to anyone near the area," he said.

It's accurate and powerful

Despite the huge power of the MOAB, it is a smart bomb with wings and grid fins for guidance, and usually explodes mere feet from the ground, an Eglin Air Force Base spokesman said after the test in 2003.

The MOAB is a thermobaric bomb -- meaning it generates both heat and pressure -- and it's not the largest weapon of its kind.

In 2007, Russia announced that it developed a thermobaric bomb known as FOAB -- the father of all bombs -- which is claimed to be four times larger than the MOAB.

Al Weimorts (left), the creator of the GBU-43/B Massive Ordnance Air Blast bomb, and Joseph Fellenz, lead model maker, look over the prototype of the bomb before it was painted and tested.

It's a show of strength

While US weapons tests are generally not televised, the very public testing of the MOAB in 2003 was a direct show of strength to Saddam Hussein and Iraqi forces. "The goal is to have the pressure be so great that Saddam Hussein cooperates," said former Defense Secretary Donald Rumsfeld in March 2003.

The MOAB was selected for its ability to generate "overpressure" -- a particularly effective method of targeting underground tunnel systems.

"As ISIS-K's losses have mounted, they are using IEDs, bunkers and tunnels to thicken their defense," said Gen John Nicholson, commander of the US forces in Afghanistan, in a statement shortly after the strike. "This is the right munition to reduce these obstacles and maintain the momentum of our offensive against ISIS-K," he said, referring to the ISIS affiliate in Afghanistan.

The MOAB had secretly been stationed in the country for "some time," according to CNN's Barbara Starr.